Sliding member and production method for same

Abstract

A sliding member has a sliding surface of a different form than a conventional sliding surface, and exhibits stable sliding characteristics even under a high surface pressure. The sliding member has a sliding surface formed on a surface of a metal base material, and includes two surface textures: a hard part and a tough part. The tough part contacts with the hard part and has a hardness lower than that of the hard part. The sliding surface includes the surface texture, in which the hard part and the tough part that supports the hard part are present in a mixed fashion with a micro-meso region level, and stably exhibits excellent wear resistance.

The invention claimed is: 
     
       1. A sliding member having a sliding surface formed on a surface of a metal base material, the sliding surface having a surface texture that comprises:
 a hard part, the hard part being a modified part obtained by subjecting the surface of the metal base material to modification treatment; and 
 a tough part contacting with the hard part, the tough part being a non-modified part that is not subjected to the modification treatment, the tough part having a hardness lower than that of the hard part, and a portion of the hard part that extends below the sliding surface is surrounded on every side by the tough part, wherein
 the hard part is either one of: (i) a nitride part subjected to nitridation treatment; (ii) an oxide part subjected to oxidation treatment; (iii) a phase transformation part subjected to heat treatment; or (iv) a size refined part subjected to size refinement treatment for crystal grains; 
 when the hard part is obtained by subjecting the surface of the metal base material to the nitridation treatment or the oxidation treatment, a concentration of nitrogen or oxygen in the hard part is 1 atomic percent (at%) or more; 
 when the hard part is obtained by subjecting the surface of the metal base material to the size refinement treatment, an average crystal grain diameter of the hard part is 400 nm or less; and 
 the tough part has the same original characteristics as the metal base material before the metal base material is subjected to any of the nitridation treatment, the oxidation treatment, the heat treatment, or the size refinement treatment, the original characteristics including at least a concentration of nitrogen, a concentration of oxygen, a phase, and the average crystal grain diameter. 
 
 
     
     
       2. The sliding member as set forth in  claim 1 , wherein the surface texture is configured such that the hard part and the tough part are present in a mixed fashion with micro-meso region level. 
     
     
       3. The sliding member as set forth in  claim 1 , wherein the surface texture is such that at least a part of the hard part is stripe-like, grid-like, or dot-like. 
     
     
       4. The sliding member as set forth in  claim 1 , wherein the surface texture is such that at least a part of the hard part extends lengthwise in a direction that is not parallel to a sliding direction. 
     
     
       5. The sliding member as set forth in  claim 1 , wherein the surface texture is such that surface area ratio (100×S1/S0) as a fraction of total surface area (S1) of the hard part to the entire surface area (S0) is 2% to 95%. 
     
     
       6. The sliding member as set forth in  claim 1 , wherein the metal base material comprises any of iron alloy, titanium alloy, aluminum alloy, magnesium alloy, or copper alloy. 
     
     
       7. A sliding member having a sliding surface formed on a surface of a metal base material, the sliding surface having a surface texture that comprises:
 a hard part, the hard part being a modified part that is formed by a process of irradiating a high energy beam on a surface part to be treated of the metal base material, while relatively moving the high energy beam, thereby to cause ablation in the surface part and to generate plasma in a vicinity of the surface part, such that the surface part irradiated by the high energy beam forms the hard part; and 
 a tough part contacting with the hard part, the tough part being a non-modified part that is not subjected to irradiation, the tough part having a hardness lower than that of the hard part, and a portion of the hard part that extends below the sliding surface is surrounded on every side by the tough part, wherein
 a concentration of nitrogen or oxygen in the hard part is 1 atomic percent (at%) or more; 
 an average crystal grain diameter of the hard part is 400 nm or less; and 
 the tough part has the same original characteristics as the metal base material before the metal base material is subjected to the irradiation, the original characteristics including at least a concentration of nitrogen, a concentration of oxygen, a phase, and the average crystal grain diameter. 
 
 
     
     
       8. A production method for a sliding member, the production method comprising an irradiation step of irradiating a high energy beam on a surface part to be treated of the metal base material, while relatively moving the high energy beam, thereby to cause ablation in the surface part and to generate plasma in a vicinity of the surface part, wherein
 the sliding member as set forth in  claim 1  is obtained to have the surface part as the hard part. 
 
     
     
       9. The production method for a sliding member as set forth in  claim 8 , wherein the high energy beam is a pulse laser having a wavelength of 700 nm or less. 
     
     
       10. The production method for a sliding member as set forth in  claim 8 , wherein the irradiation step is a step that irradiates the pulse laser to the surface part while partially overlapping irradiated regions by pulse light beams adjacently oscillating. 
     
     
       11. The production method for a sliding member as set forth in  claim 8 , wherein the irradiation step is such that a pulse lap ratio is 10% to 90%, the pulse lap ratio being a fraction that irradiated regions by the pulse light beams are overlapped.